Refrigeration requirements in both commercial and residential buildings frequently necessitate the maintenance of different temperatures at different locations in the building. Frequently, such needs were met by having a separate insulated enclosure and refrigeration unit, including compressor, condenser and evaporator, at each location. For example, a commercial establishment might have a wide variety of refrigeration needs, such as, chilling stored or prepared food, chilling bottled beverages at one or more temperatures, chilling keg-stored beverages, room air conditioning, etc. The use of individual refrigeration systems for each of the different tasks is obviously expensive and wasteful.
Wastefulness of the type described is further compounded by the fact that some condensers necessarily dump heat into areas or spaces that are cooled by other refrigeration equipment. For example, a refrigerator for food that is located in an air conditioned space is ejecting heat into that space. As a result, the air conditioning load is increased because the heat generated by the food refrigerator must be processed a second time.
It is well known that a single large compressor/condenser unit is more efficient than multiple small compressor/condenser units such as would be required in a system using multiple refrigerators. Accordingly, efforts have been made to achieve differing temperatures from a single compressor/condenser, but those efforts have been characterized by a number of disadvantages and limitations. Heretofore, the method employed to maintain different temperatures from a single compressor/condenser utilized a separate evaporator for each temperature requirement. Each of the evaporators was controlled by an expansion valve and all evaporators but the one required to be at the lowest temperature were equipped with a constant evaporator pressure control valve. The drawbacks of that type of system included the difficulty of balancing the individual evaporators, charging the entire system, and adjusting the multiple constant evaporator pressure control valves. In addition, that type of system required large quantities of refrigerant because of the extensive piping requirements.
There was disclosed in U.S. Pat. No. 4,949,552 a cooling system for maintaining desired drinking temperature of a beverage dispensed at locations remote from the place of beverage storage. That system efficiently utilized a single compressor/condenser unit to chill a minimal supply of glycol-water and the glycol unit coolant was flowed through tubing in contact with the beverage tubing in the line run. The patented system maintained the beverage at all dispensing stations within a narrow desired temperature range, or at substantially uniform temperature.
Peculiar problems of temperature maintenance apply to the dispensing of beer because different brewers insist that their beer tastes best and, therefore, must be served at certain optimum temperatures. For example, British brewers suggest that their beers and ales be drunk at temperatures between 52.degree. and 55.degree. F. Most German brewers insist that their beers be drunk at between 45.degree. and 48.degree. F. American and Australian beers, by contrast are recommended to be drunk at below 40.degree. F. An establishment serving many brew varieties would be confronted with the problem of maintaining the different serving temperatures as indicated.
There thus exists a need for a cooling system which operates efficiently from a single, or perhaps two, compressor/condenser units, but has means for selectively maintaining different temperatures within wide desired ranges. Similarly, a need exists for a system capable of removing heat from one or several spaces in an efficient and cost effective manner.